[skj]

A brief dig didn't get me to any cited data. They refer (without link) to "Global Rich List", which might be http://www.globalrichlist.com/.

Scrolling through all their infographics, I finally get to this: "For the income track, we've used the most recent (2008) statistics from the World Bank, based on household surveys. Here we rank you against the entire world population at the time of the surveys, estimated at 6.69 billion people."